Sinus Pauses / Asystole

Description

For expediency, this section is titled sinus pause/asystole. Sinus pause and sinus block are slight variations of the same rhythm, both of which may lead to an asystole which is an absence of electrical activity in the heart. However, there are other causes of asystoles as well. First we discuss sinus pause, and further down the page, asystoles.

Sinus Pause/Sinus Block

Sinus pause describes a condition where the SA node fails to generate an electrical impulse for what is generally a brief period of time. In the above example, the initial rate is 88 beats per minute (the first two beats are normal), then there is a 1.8 second sinus pause before the heart resumes, initially at a somewhat slower rate of 52 beats per minute. A related rhythm is SA block which is often hard to distinguish from a sinus pause. In SA block, the SA node creates an impulse, but it is blocked from leaving the SA node. The differences are beyond the scope of this discussion.

Patients who have sinus pauses may complain of missed or skipped beats, flutters, palpitations, hard beats or may feel faint, dizzy or lightheaded or experience a syncopal episode (passing out). Frequent pauses would heighten these symptoms. This is a result of patients actually missing or dropping beats. Obviously, if the heart misses a beat, blood does not flow during that time period resulting in a lack of oxygen or perfusion throughout the body.

Treatment and prognosis depend on the cause and cardiac status of the patient. This condition may be drug induced or it may be a result of cardiac disease. Treatment may involve the use of medications or the use of a temporary or permanent pacemaker.

Asystole

The above is an example of a a 6.3 second asystole, in this case caused by sinus arrest with no backup pacemakers taking over. The first beat is normal, the second beat is a PVC, then there is 6.3 seconds of no electrical activity in the heart, followed by a relatively normal looking beat at the far right side of the strip (although technically it is a junctional escape beat, e.g. the impulse originated in the AV junction, not the SA node). Although the above example shows no electrical activity during the 6.3 second asystole, you may also have a similar asystole where there are P waves throughout the asystole but no QRS complex as a result of complete AV block with a failure of the backup pacemeker (all cells in the heart can act as backup pacemakers to the SA node). The result for the patient is the same; severe lightheadedness, dizziness, near sycnope or a syncopal or passing out epsiode. Depending on the cause, medications or a permanent pacemaker is indicated.